影响反应时间的因素？
参考答案：
①感觉器官的影响；
②刺激信号的性质及强度的影响；
③刺激的清晰度和可辨性的影响；
④动作方向。
He _______ me five dollars for it, but at first he said to me the work would be done ______.
A．charged ; free of charge
B．charged for ; charged for nothing
C．charged ; out of the charge
D．charged to ; free of the charge
怎样保证水稻插秧质量？
